Radio goniometer



y 15, 1956 CARL-ERIK GRANQVIST 2,746,038

RADIO GONIOMETER Filed Nov. 19, 1951 2 j/O M 06 ZZ r l T12 a 2 al 02 z z, 4

1/ .1/ 1/ 1/.1/ l/i a T -r r T T 'r r ///r \IZ Z 50 INVENTOR ATTO EYS United States Patent 2,746,033 RADIO GoNioMErEn CarLErik Granqvist, Lidingo, Sweden, assignor to Svenska Aktiebolaget Gas-accumulator, Lidingo, Sweden, a curporation of Sweden Application November 19, 1951, Serial No. 257,137 11 Claims. (Cl. 343-124) For direction finding with radio waves generally two dilferent methods are used, viz. partly with turnabie antenna system, mostly a frame antenna, partly also'with angularly placed fixed directional antennas, the down leads of which are connected to corresponding means on the primary side of a goniometer. The primary and sec ondary sides of the goniometer are thereby mutually turnable, and the desired direction to be found will then be given by the setting between the primary and the secondary side of the same angular position which should have been the setting angle in the case of direct direction finding with turnab'le antenna system.

in present recommendations for radio equipment for air fields it is proposed to use an automatic direction finding system with cathode ray oscillograph indicator, intended for a frequency range within the meter range, that means 118-132 megacycles a second, corresponding to 2.25-2.35 meters. It is true that there has also been proposed a somewhat Wider wave-length range of 1.92- 2.73 meters, corresponding to 110-156 megacycles a second, but the difi'iculties encountered in the one case, remain mainly unchanged also in the other case.

Rotational antennas could scarcely be used, owing to the high rotation speed in combination with the dimensions the antenna system must have for the frequencies in question, because known automatical direction finding systems are not adapted to such a speed. The antenna systems can in such cases, not Without great difficulties, be dimensioned in such a way that they stand the mecha-n ical strain due to rotation. Even if one should manage to'overcome this problem, a great air resistance will'be created, and for this reason the motor used :for driving the antenna system will be big, heavy and bulky, and thus undesirable when moving the reception apparatus from one place to another one. Of course, most reception apparatus used for air fields must be transportable.-

Therefore, to a great degree, goniometer reception has become advisable, but for practical reasons this must preferably be capacitive. However, capacitive goniometers always have great capacities to ground which must be compensated for by means of inductances, and possibly also be damped by resistances, whereby the frequency range is limited and, simultaneously, the goniometer losses will be great. Furthermore, the work of proper balancing will be very difiicult.

The present invention refers to a goniometer intended for short wave purposes of so-called linear type, that means a goniometer in which the primary and the secondary means, respectively, consist of real, possibly shortened conductors, movable .in relation to each other, According to the invention, the high frequency feed terminals on the conductors are so arranged that they will be at greatest possible mutual distance. Further, lines are provided which are parallel or substantially parallel to the antenna system. Thus if the antenna system is formed by a four-polar dipole antenna system, four-lines are provided in such a position that each line will be 90* mechanically displaced-in relation to'the other lines, suit-.

2,746,038 Patented May 15, 1956 ably together forming the stator, whereas the rotor part is formed by one line, or alternatively, two lines mutually displaced by 180.

According to a specific form of execution of the invention the lines in the goniometer are shortened byapplying a number of discreet capacities, divided along the lines.

The arrangement of the goniometer will, in other respects, be evident from-the following description in connection with the attached drawing, in which Fig. l-sho ws a diagram for the explanation of the general function of the line-goniometer, Fig. 2 shows a variation of the diagram according to Fig. 1, Figs. 3 and 4 show two arrangements of the line-goniometer, without regard to the lines being shortened or not, Fig. 5 shows"a*modified line, contained in the diagrams according'to Fig. l or 2, but capacitively shortened, Fig. .6 shows a capacity element for providing the shortening of the line, and Fig. 7 shows a line goniometer according to Fig. 1 with shortened line length.

The principle of the line-goniometer is that electrical resonance lines are used for primary means and secondary means, respectively, in a capacitive goniometer. According to what has been experimentally found, these need not be exactly tuned to the received wave-length, but in the wave-length ranges which are of interest in this case. in this case, it is quite sufiicient if the linelength is adapted according to a wavelength approximately in the middle of the wave-length range to be received. For instance, a fully usable line-goniorneter may be built on basis of the assumption that the wavelength is 2.20 meters, corresponding to a frequency of "136 megacycles a second, if one intends to use the goniometer for direction finding within the wave-length ranges mention in the preamble of this specification.

According to Fig. 1, one of the primary goniometer means is made in the form of a line of one quartero'f a wave-length, that means in the chosen example, of 55 centimeters. Thisline is indicated 10, its characteristic is indicated by Z01, and its input impedance with'Zi. The corresponding secondary goniometer element is indicated 11, its characteristic with Zo2, and its end impedance with Z2. The two lines are mutually coupled by means of the mutual inductance, the magnitude of which is indicated with M. The principle of this goniometer is now, "that by means of the mutual inductance M voltages should be introduced into the secondary elements in the same way as will, for instance, take place in the usual inductive coil goniometer. One therefore provides four primary goniometer means 12, 13, 14, and 15, as evident from Fig. 3, which are terminated by the corresponding fourterminal antenna. This'has been assumed to be a dipole antenna, containing 'four dipole pairs, provided in the four cardinal directions, and over suitable transformers connected to the four lines in the primary part of the goniometer, as evident from the drawing figure. The secondary part consists of two corresponding lines 16 and 17, respectively, applied on a rotor part -18, 'turnable about the shaft 19. I It is further assumed that the line 11 is terminated by an end impedance Z2'=Zo2, as far as the impedance disturbs the inductive transfer of voltages.

frequencyrange question, if this is, for instance, as p mentioned in the preamble, 110-156 megacycles a second, and if the line is tuned for an intermediate frequency of 136 megacycles a second, then the impedancevariation will only be minus 37.5% and plus 32%, respectively, which is wholly allowable. 7 Some difficulty may, however, occur in providing a satisfactory mutual inductance in an arrangement, built up according to Fig. 1. But this difficulty is easily done away with by displacing the lines in such a way that they' partly overlap each other, as indicated in Fig. 2. If the electrical overlap angle is a, referring to the assumption that the total length of, the primary line is 90", and if further thecoupling factor between the lines is K, then i greater coupling rates than E Also the overlap angle must not exceed 45 or the half length of the primary line, because in such case a capacitive coupling will result which will be so strong that. it

A line goniometer of the kind described usable, but in practice it has proved to be somewhat handy, owing to its obtaining rather big dimensions. It is therefore an advantage to shorten the line length and this may also take place according to a further development of the present invention. By way of an explanation of this, it is referred to the following investigation:

If ,the line according to Fig. 2 is made air insulated and. has a characteristic indicated. Z, then according to known relations its inductance per foot will be 1.0161

micromicrohenry andits capacity with discreet capacities 26, one per unit of length, thecapacity per unit of length-will obviously be above is fully adaption over a great frequency range. A suitable value for Z; is approximately 4Z0; or with other words 50 to 100 ohms.

If the capacity load is builtup in a suitable way, a further advantage will be obtained, viz. a capacitivescreening of the line as a whole,.so that the two lines are screened mutually against capacitive transfer of voltages, whereas, on theQother hand, the inductive transfer of voltages will passundisturbed.

The distributed, distinct capacities could suitably be I provided by arranging "a number of discs of the type, shown in Fig. 6, These discs are placed in parallel to each other atisuitable distances. The discs are provided with holes 27, through which the line conductor 28 is carried. The discs should, of course, be connected to ground.

Although the capacitive shortening of theline has above in first place been described in connection with the primary line 10, it is evidentthatsa'me shortening'method could be used with same advantage-also for the secondary line. i 7 t The line-goniometer, shown in Fig. 7, is made in accordance with the principle shown in Fig. 3, although in this line-goniometer capacitive shortening of the lines lines are preferably made of metal pipes, fixed in plates has been used as described above. Fig. 7 thus forms a section through the arrangement according to Fig. 3, so that the lines visible'in Fig. 7 are formed by the lines 12,14, 16, and 17. The lines 12 and 14, as well as the not shown lines 13 and 15, thus are applied on the stator part, which is carried-by a capacitively screeningcasing 29. In the casing 29, discs of metal 30 are fixed, provided with holes, arranged in a line, the lines 12., 13, 14, and 15 being carried through said holes. The proper 31 on a shaft 32for the rotorpart and to the casing 29, respectively.

As evident from-Fig.7, the ground connected ends of the stator lines 'aredirected to the right, whereas their high frequency'orhigh voltage ends are'directed to the left. On the other hand, the line barsof the rotor are turned in the opposite direction. They are grounded by connection between the disc-31 at their terminal, in the drawing turned to the left, whereas to the right they are provided with a line terminal 33, which is carrying the in which equation Cb indicates the additional capacity per unit of length.

The propagation speed on line 10 will then be 12 ii"? V 1.016 /lC -m V In order to get down to, for instance half the speed of light, Cb should be 3.048/Z micromicrofarads per foot, as is easily calculated from the above equation.

The characteristic of the unloaded line being a/f/E, the v new characteristic will be value of the line characteristic Z01 results in a better;

high voltage current in relation to ground. The voltage in the line terminal may, of course, be taken out through any arrangement suitable for this purpose, directed to the right, but this may easily result in certain disadvantages, amongst others to the effect that the voltages would be fed 'to' the primary side or put out from the secondary side at ditferentfends of the goniometer, whereby the mounting of this goniometer would be more difiicult, and further that the screening against ground would be unsatisfactory. As a matter of fact, this is so important that one has provided a special screening plate 34 at the open end of the stator. It is thereforeadvantageous to conduct the voltage output from the line terminal 33 through one of the hollow pipes 16 or 17, or if full symmetry'is desired in parallel through both of these pipes.

In the arrangement shown-in Fig. 7, the conduit 35 is carried through the pipe 17 as indicated by dotted lines.

It is of' great importance for the decrease of the capacitive couplingthat the high voltage terminals of the line conductors are in this way directed in different directions. The capacitivecoupling is further decreased thereby that the high voltage terminal of the rotor part or of the secondary part is extending into a recess 36 past the grounding end of theline conductor of the stator part or the primary part.

However, it is desired not only to have a broad frequency range, a good transmission and symmetry in the cardinal directions and intercardinal directions, which will be obtainedby means of the arrangement shown in Fig.7, but in order to make the reading more easy or for improving the function of the automatical means at v automatical directionfinding; it.is;also desired to get a reasonably good sinus variation of the voltage during the rotation of the rotor with a constant speed. This sinus variation can not quite simply be obtained with the arrangement shown in Fig. 7, but it may be obtained with a slight modification thereof. This modification is schematically shown in Fig. 4 in a way, approaching the method of explanation used in Fig. 3. The voltage division will, in this arrangement, not be exactly sinusformed, but by way of empirically finding the most suitable division between the different lines, one may get to a division curve, so little diifering from the pure sinus curve that it will be quite satisfactory for the needs present in practice.

According to Fig. 4 each of the different line conduits is broadened in such a way that it is replaced by two line conductors, connected in parallel and placed at given distances from each other. Thus there are two line conductors 12' and 12", corresponding to the line conductor 12 in Fig. 3, and in a corresponding way two line conductors indicated with prime sign and two line conductors indicated with a secondary sign, respectively, are corresponding to each of the line conductors 13, 14, 15, 16, and 17.

The angle between the different line conductors must, as a rule, be determined experimentally. The following figures give, however, a statement of a dimensioning which has been found to be good: The statorand rotor lines are made of pipes of 6 millimeter diameter, and the radial difierence between the centers of the stator pipes and the rotor pipes was 12 millimeters. The angular difference between two pipes coupled in parallel, and belonging to the stator, was 22.5, and the corresponding angular difference of the rotor was A goniometer of the above described kind is, of course, not only usable for direction finding purposes, but it may also be used in any case, where a gondiometer is commonly used, for instance as a balanced modulator. It may further be used as a modulation or codifying element in direction radio beacons of the so-called complementary code type (E-T-beacons or A-N-beacons respectively) as well as in a plurality of other cases. The frequency range is not limited to the frequency bands mentioned above, but in tests very good results have been obtained within frequency ranges of a width from up to 3,000 megacycles a second, whereby the line goniometer was dimensioned for 100 megacycles normal frequency.

What is claimed is:

1. A radio goniometer, especially for short-wave purposes, oompn'sing, a plurality of electrical oscillation lines in the form of straight conductors, mutually parallel and in mutual inductive coupling, one portion of these electrical oscillation lines being stationary to form part of a stator, the remaining portion of the oscillation lines being rotatably mounted to form part of a rotor, the high voltage terminals of said stationary lines being located at one end of said stationary lines, and the high voltage terminals of said rotatably mounted lines being located at the opposite end of said rotatably mounted lines.

2. A radio goniometer according to claim 1, in which the stationary and rotatable oscillation lines are parallel to each other over at least a portion of their lengths, so that a projection of one such oscillation line onto another oscillation line will partly coincide with said oscillation line.

3. A radio goniometer according to claim 2, in which the oscillation lines belonging to the rotor are located with their high voltage terminals in opposite direction to the high voltage terminals of the oscillation lines belonging to the stator.

4. A radio goniometer according to claim 3, and a screened casing for said oscillation lines, said casing capacitively limiting the goniometer, means forming a recess in said casing, the high voltage terminals of the oscillation lines of the rotor only being located in said casing.

5. A radio goniometer according to claim 1, in which the oscillation lines are made of pipes, and a voltage output conductor from the high voltage end of the rotor part is carried through at least one of the pipe-formed oscillation lines of the rotor part.

6. A radio goniometer according to claim 1, in which each oscillation line in at least one of said rotor and stator has a length of one quarter of the wave length at a mean frequency within the frequency range for which the goniometer is to be used.

7. A radio goniometer according to claim 6, and capacitances distributed along said lines and connected to ground, whereby the mechanical length of the oscillation conductors is shortened in relation to the electrical length.

8. A radio goniometer according to claim 7, and means disposing said capacitances with respect to said lines to serve as a capacitive screening for the oscillation lines.

9. A radio goniometer according to claim 8, in which said capacitances comprise even discs, running perpendicularly to the longitudinal direction of the oscillation lines, and in which holes are formed for carrying the oscillation lines.

10. A radio goniometer according to claim 9, in which each of said oscillation lines is composed of at least two conductors connected in parallel, said conductors being located in a suitably chosen angular displacement in relation to the turning shaft of the goniometer for obtaining a closely sinus-formed division curve at the rotation of the goniometer.

11. A radio goniometer according to claim 10, in which there are four symmetrically applied oscillation lines in the stator part of the goniometer and two diametrically applied goniometer means in the rotor part of the goniometer, the conductors of the stator being provided with an angular displacement of approximately 225 and the conductors of the rotor part being arranged with an angular displacement of approximately 45".

References Cited in the file of this patent UNITED STATES PATENTS 2,465,353 Chesus et a1. Mar. 29, 1949 

